Acute cerebellar ataxia is a benign syndrome usually occurring after an acute febrile disease. In a few cases neuroradiological investigations reveal cerebellar alterations. Clinical and neuroradiological involvement of the brain stem has rarely been reported in the literature. We present five cases of acute cerebellar ataxia. In two cases the cerebellar symptomatology was associated with neurological signs of brain stem involvement. CT scans did not show any pathologic findings in three patients. MRI disclosed cerebellar or brain stem alterations in all the patients. Clinical and neuroradiological findings allow differentiation of this pathologic entity from other demyelinating or dysmyelinating diseases. The value of MRI in detection and localization of the lesions and in following their evolution is emphasized.